Transformer bushing



April 6, l1943. A.. A. sKvoRTzol-'F -TRANSFORMER BUSHING Original FiledOct. 18, 1938 WITNESSES:

ATTO

Patented Apr. 6, 1943 TRANSFORMER RUSHING Alexander A. Skvortzof,Sharon, Pa., assigner to Westinghouse Electric & Manufacturing Company,East Pittsburgh, Pa., a corporation of Pennsylvania Original applicationOctober 18, 1938i, Serial No. 235,611. Divided and this application July31, 1940, Serial No. 348,718

2 Claims.

This application is a division of .my copending application Serial No.235,611, le-d October 18, 1938 (Patent No. 2,228,089), and theinvention, as in the parent case, relates to bushings for insulating theconducting leads of high-tension electrical apparatus, such astransformers and circuit breakers, and has particular reference to anim* proved cap for closing the exposed end of such bushings.

Bushings of the type contemplated usually comprise an elongatedcylindrical member of insulating material, such as porcelain, throughwhich the conductor or lead from the apparatus extends to be connectedat the upper end of the casing to a terminal which, in turn, is to beconnected to an electrical circuit. The conducting lead in many cases issurrounded by a hollow metallic stud or the stud itself may be used asthe conductor. In either event, by reason of the difference in thecoeicient of expansion between the metallic and porcelain parts, it isdiicult to maintain the bushing fluid tight and to prevent breathingupon change in temperature. rlhe bushing is usually filled with adielectric uid, which may be oil or a gum, and upon breathing cyclesmoisture may be drawn into the bushing with resultant damage. l

It is usually undesirable to have communication between the hollow studand the interior of the bushing, and this is particularly diicult toprevent because the thermalexpansion and contraction of the hollow studlongitudinally thereof makes it necessary to terminate the stud withinthe bushing'and allow space to permit such expension and contraction.

Itis an object of the present invention to provide a bushing terminalcap, in conjunction with a bushing having a hollow metallic stud, inWhich means is provided to prevent communication between the interior ofthe stud and the interior of the bushing in spite of contraction andelongation of the stud under the influence of temperature changes, andat the same time to provide a simple construction, which facilitatesassembly of the bushing for accomplishing this result.

Other objects of the invention will be apparent from the followingdescription in conjunction with the accompanying drawing in which thesingle gure' of the drawing is a view in vertical section of the cap i abushing of the type contemplated, including a part of the bushing, apart of the bushing being broken away.

Referring to the drawing, the bushing may comprise a cylindrical casing2 of dielectric ma terial, such as porcelain, usually having a pluralityof flanges 4, only one oi which is shown. The upper end of the bushingcasing 2 is surmounted by a cap E, which rests upon the end face of theporcelain casing 2, being spaced therefromby gaskets 'I and 8 ofdifferent compressibility so that one acts as a compression stop for theother. rIhe top of the cap 6 is surmounted by a terminal I0 to which theexternal electrical circuit is to be connected.

By way of example the present invention may be used with a bushing ofthe condenser type in which alternate layers of conducting andinsulating material are wound upon a hollow metallic stud I2. In thedrawing, the condenser wrapping is indicated at I4, the construction andassembly being substantially the same, as shown in the patent to E. E.Arnold et al. No. 2,088,502, issued July 27, 1937. It is intended,however, that the invention is applicable to bushings of other than thecondenser type. f

The cap 6 comprises a main body portion of substantially cup-shapehaving a base portion proportioned to rest upon the end face of theinsulating shell or casing 2. The body portion is provided with acentral aperture through which loosely extends the upper end of themetallic stud I2, the latter terminating within the confines of the cap.The cap is provided with a cover IG suitably bolted thereto to effect afluidtight joint and has a central extension I8 surmounted by theterminal I0 secured to the extension I8 in a iiuidtight manner.

The conducting lead 2l] from the electrical apparatus with which thebushing is to be associated, is drawn up through the stud I2 and issuitably secured to a block 22 threaded to the interiorl of the coverextension I8 by means of a nut 2,4.

Upon variations in temperature, relative movement between the porcelainshell 2 and the stud I2 will occur. The relative movement is quitesmall, but unless provision is made for it, the destructive forcesresulting will, upon contraction of the stud, tend to crush theporcelain or crack the metallic parts of the bushing, and uponelongation, the various gasket joints may open, destroying thefluid-tight character of the bushing. In order to take care of thissituation, a fitting 26 is threaded to the upper end of the stud I2, andthen preferably brazed to it, and is provided with a plurality ofapertures through which bolts 28 extend, terminating at their lower endsin sockets 30 cast into the base of the cap 6. It is intended that thefitting 26 is preferably in the form of a spider and that the bolts 28will extend loosely through their respective apertures. The number ofbolts and springs required must be determined by the size of thebushing, four being indicated, by way of example in the drawing.

Each bolt 28 is provided with a square flat plate 32 adjacent its lowerextremity to constitute the seat for a helical spring 34 which surroundsthe bolt. The upper end of the spring is in engagement with the underface of the fitting 26. By this means` when the springs 34 are undercompression, they will transmit a force from the stud 2Q through thetting 26 and bolt 28 to the base of the cap 6, which will maintain thegaskets 1 and 8 under compression, as well as the gasket 8 at the lowerend of the porcelain shell. The desired pressure may be maintained byadjustment of the bolts 28, the plates 32 being square will engage theside wall of the cap and not turn with the bolts. gree of compression ofthe springs 34 should be so chosen that they will always be undercompression in spite of elongation of the stud I2 throughout the normaltemperature range encountered in service, and throughout such range thesprings are positively retained in operative position by the bolts 28.

In order to prevent communication between the interior of the stud I2and the cap 6, a tubular flexible member 40 of a fluid-imperviousmaterial is secured to the upper end of the stud l2 in fluid-tightmanner by means of a clamp 42, and the upper end of the flexible member40 is clamped between a depending conical flange 44 on the cover I6 andthe lower beveled edge of a clamping member 46, which is actuated toclamping position, as indicated, by screwing down block 22 to an extentnecessary to obtain a hermetic seal.

The flexible member 40 may be of any desired material so long as it isfluid-impervious, retains its flexibility over a reasonable period, andwill not deteriorate under the influence of the oil, gum or othercompound with which the bushing is usually lled. There are on the marketmany types of synthetic rubber, and fabric impregnated therewith whichare suitable for this purpose, and I have found that one of suchmaterials which is satisfactory is sold under the trade name Duprene.

By means of the construction described, Iit should be apparent that theinvention contemplates an unusually simple construction but at the sametime takes care of the many severe conditions encountered inthe normaluse of bushings of this character.

Also, the construction results in a simple assembly operation involvingno soldered joints and a minimum of parts. In such assembly operation,when the cap 6, with the cover I6 removed, is placed in position, thefitting 26 may readily be screwed into place and the bolts 28 insertedwith the springs 34 and plates 32 before the springs are placed undercompression. The bolts 28 may then be screwed down to draw up the plates32 to place the springs 34 under the desired degree of compression. Thismay be accomplished by a simple wrench rather than having to resort toexpensive jigs to place the The delil springs under compression beforethey are placed in position in the cap. The lower end of the flexiblemember 40 may then be clamped to the top of the stud l2 by means of theclamp 42, and it is of suliicient length that if the cover I6 were inposition, it would extend into the cavity defined by the dependingflange 44 on the under-side of the cover. The clamping member 46 is theninserted into the end of the flexible member but not sufficiently todeform such member, and the cover is then placed in proper position andbolted. The flexible member now extends into the cover cavity and theclamping member 46 extends into the cover extension 24. The block 22 isthen screwed down to expand the upper end of the flexible member 40 intocontact with the flange 44 to complete the clamping and sealing action.The conductor 20 is then shed through and secured to the position shownand the terminal member l0 may then be bolted in position to completethe assembly. The disassembly for inspection or repair is equallysimple.

Quite obviously, the design described and shown may be varied to takecare of various conditions encountered in service, .and it is intendedthat the invention is not to be limited except as imposed by theappended claims.

I claim as my invention:

1. In a bushing for high-tension electrical apparatus including acylindrical casing of dielectric material having a hollow stud extendingtherethrough and projecting beyond an end thereof, a hollow capenclosingr the projecting portion of said stud including a coveroverlying the end of the stud, a flexible tube of fluid-imperviousmaterial having one end embracing the end of said stud and means forsecuring it thereto, a cylindrical flange integral with said cover anddepending adjacent to and extending pe- -ripherally around the other endof said flexible tube, an opening through said cover axially of saidcylindrical flange, and means extending through said opening intoengagement with said other end of said tube for expanding the latterinto intimate peripheral engagement with a wall of said cylindricalflange.

2. In a bushing for high-tension electrical apparatus including acylindrical casing of dlelectric material having a hollow stud extendingtherethrough and projecting beyond an end thereof, a hollow capenclosing the projecting portion of said stud including ,a coveroverlying the end of the stud and secured to the cap in fluid-tightrelation, a exible tube of fluid-impervious material having one endembracing the end of said stud and means for securing it thereto, acylindrical flange integral with said cover and depending adjacent toand extending peripherally of the other end of said flexible tube, anopening through said cover axially of said cylindrical flange, and meansextending through said opening into engagement with said other end ofsaid tube for forcing the latter into intimate peripheral engagementwith a wall of said cylindrical flange and means for closing 'saidopening in fluid-tight relation.

ALEXANDER A. SKVORTZOFF.

